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I observed the foraging behavior of four warbler species (Dendroica petechia, Oporornis tolmiei, Geothlypis trichas, and Wilsonia pusilla) in the summer in Wyoming and in the winter in Nayarit, Mexico. Of six variables (absolute foraging height, relative foraging height, vegetation density, horizontal foraging position, feeding method, and foraging substrate) believed to be potentially important in distinguishing the warbler species ecologically, the two foragingheight variables provided the greatest separation of the four species in both summer and winter. An analysis of the behavioral similarity of each species from summer to winter revealed that feeding method was the least changed behavior and that absolute foraging height involved the greatest behavioral flexibility. The behaviors that are most flexible are possibly the least well tied to the birds' morphology and are also the ones that have been shown by other workers to reveal the effects of competitors through "niche shifts." Therefore, ecological relationships among coexisting species (in terms of overlaps or positions in niche space) may never be fully derivable from morphological information alone.


Electronic version of article available from JSTOR.


©1981 University of California Press

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